Summary
Measurement of heparin ex vivo is usually with reference to standard curve prepared
with a “spiked” normal human plasma pool (NHP). When the calibration curve was prepared
by addition of heparin to whole blood before plasma separation, although the linear
relationship was maintained the slope was increased in comparison to the classical
standard calibration curve. It is concluded that the preparation of the calibration
curve by addition of heparin to NHP may give erroneously high heparin levels in treated
patients’ plasma, leading perhaps to inappropriate dosage. It was also observed that
when heparin was added to blood of different haematocrit (prepared by addition of
washed RBC to plasma) and plasma prepared, the subsequent APTT was decreased with
the fall in haematocrit; suggesting that the laboratory monitoring of heparin treatment
should take into account the patient’s haematocrit.
Keywords
Heparin assay - LMW heparin - Haematocrit - Heparin activity
